(1) Field of the Invention
The invention refers to a derived timber board with a surface coating applied at least in parts and a method for applying such coating.
(2) Prior Art
Derived timber boards with a surface coating, which is usually applied to the upper side, as the case may be, also to the underside and the lateral surfaces, are known for many purposes. Floor panels made of derived timber board are gaining in importance, although this also applies to ceiling panels and wall panels, derived timber boards for room dividers and suchlike. It is common to use impregnates in order to obtain a resistant surface coating, which in the case of floors, is also scuff-resistant.
Impregnates are special papers impregnated with synthetic resin. The synthetic resins placed in the paper are cured until the papers are dry and suitable for storage. Following application to the derived timber boards, the impregnates are further cured under the influence of pressure and temperature. Pressure and temperature are normally applied in presses. During this process, the synthetic resin, which softens prior to final curing, flows through the paper frame to form a layer, which coats the surface of the derived timber board where the impregnate has been applied.
Depending on demands, the impregnate can comprise a paper printed with decorative elements. Corundum can be incorporated in the impregnate as an agent against scuffing.
The production of impregnates is elaborate and costly, particularly due to the expensive special papers, which serve as a base material for synthetic resin, the decoration and, if necessary, for corundum.
Therefore, methods have been developed for applying decorative elements directly to the surface of derived timber board without the use of carrier paper and also synthetic resins and, if necessary, corundum. This is exemplified by DE 27 18 705 A1, in which is described the application of melamine resin to chipboard. The melamine resin is provided with pigments or filling substances if necessary.
In detail, though, difficulties occurred when the predominantly thermosetting synthetic resins were applied, particularly in the processing of well suited and cost-advantageous aminoplastics. Until now, the synthetic resin, e.g. a melamine resin, was applied to the special paper and precondensed. Drying of the impregnate led to shrinkage as a result of a reaction of the synthetic resin. The special paper also participated in such change of form. No more significant form changes were observed when the impregnate was being pressed to the derived timber board.
When applying the synthetic resin directly to a derived timber board surface, the synthetic resin can, in principle, be applied sparingly, depending on the desired layer thickness. When applying a relatively thin coating directly, however, the fact that the synthetic resins do not always form the desired, uniform layer on the surface of the derived timber board is disadvantageous. The surface coating-exhibits a non-uniform layer thickness.
Beyond that, the shrinkage of the synthetic resin while curing turns out to be problematic. As a result of the strong shrinkage force created during curing, the curing synthetic resins exert a strong tensile force in the plane of the coated surface of the derived timber board, which partially leads to deformations, which make further processing of the coated board impossible. In addition, in combination with the relatively weak adhesive force of the thermosetting synthetic resins on the board, the strong shrinkage force causes coating fragments to pop off. The deficient film formation, which is observed in particular when melamine resins are used, causes parts of the synthetic resin to come off of the derived timber board during curing when a coating is applied directly to the surface of a derived timber board.